Metal deforming – With use of control means energized in response to activator... – Metal deforming by use of roller or roller-like tool element
Reexamination Certificate
2000-10-03
2001-11-13
Tolan, Ed (Department: 3725)
Metal deforming
With use of control means energized in response to activator...
Metal deforming by use of roller or roller-like tool element
C072S012200, C072S201000, C072S247000, C072S366200
Reexamination Certificate
active
06314776
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rolling mill stand having rolls that are axially slidable with respect to each other, more particularly, to work rolls or intermediate rolls having a seventh order polynomial surface profile which together form an adjustable gap with a sixth order profile.
2. Prior Art
Strip product such as aluminum is typically rolled in a four high or six high rolling mill stand. Recently, the demand for thin aluminum strip product has increased, particularly for the beverage can industry. For such applications, the strip must be hot rolled to as thin as 0.090 inch with minimal variations in flatness. Flatness defects should be avoided and the strip should have a constant thickness over its entire length. To avoid unevenness of the strip, it is necessary to roll the strip uniformly over its width, so that internal stresses are avoided which could lead to undesirable undulations in the middle area, the edge area or the quarter area of the strip. Such internal stresses typically result in edge cracking during hot rolling and subsequent cold rolling which requires that sections of the coil with large cracks be cut away and scrapped. If edge cracking occurs in the middle of a coil, the entire coil may need to be scrapped.
Strip flatness defects are due in part to the forces exerted on the rolls from the strip, referred to as bending deflections, and alterations in the diameter of the rolls which develop across the length of the rolls. These alterations are caused by the force of the strip flattening the rolls and by thermal expansion of the rolls which creates a thermal camber on the roll surfaces. The mid-point of the roll is the hottest, hence the thermal expansion of rolls is greatest at the mid-point of the rolls and decreases towards the ends of the rolls. The resulting roll gap profile is uneven across the length of the rolls which creates uneven rolling across the width of the strip. Uniform rolling can only occur if the roll gap profile under load is properly adjusted by means of adjusting mechanisms.
One such adjusting mechanism is a bending jack. Bending jacks are applied to the neck of the roll to exert a force to compensate for the bending deflections and thermal camber. The jacking force is designed to counter the vertical shift in the roll surface at the roll mid-point by bending the ends of the roll, so surfaces of the ends of the roll are in the same plane as the roll mid-point. While bending jacks compensate for bending deflections very well because they are both parabolic in their functional form the roll gap profile may still not be sufficiently corrected to produce thin strip with acceptable flatness in situations where the thermal profile of the work rolls has a large magnitude and steep drop off at the edges of the strip. In these situations, use of parabolic actuators such as bending jacks and traditional ground work roll crowns will not provide the required compensation and quarter buckle flatness defects will appear in the sheet. Additionally, use of bending actuators with fixed roll crowns may not provide adequate adjustment range for mills that process a wide range of products of different material hardness and strip width.
One system for accommodating the characteristics of various rolled products and varying thermal crown on the work rolls is described in U.S. Pat. No. 4,881,396. Axially slidable rolls are shaped in such a way that the effect resulting firom the contours of two rolls can be determined by the relative axial displacement of the rolls. A roll gap of various parabolic and quartic shapes can be created by adjusting the shift position of the rolls to tailor the mill to the characteristics of the product being rolled. Bottle shaped rolls may be operated to provide a continuously variable crown (CVC) capable of compensating for parabolic bending over the entire length of the roll bodies and the effect of thermal camber build-up if the magnitude and steepness are not too great and the strip is fairly thick. However, while such CVC rolls provide more flexibility and actuator range to roll a broad product mix, they may not completely compensate for the thermal profile of the roll and still may produce wavy sections of the strip.
The '396 patent further describes using rolls having profiles described as fourth order polynomials to reduce the waviness in the edge or quarter areas of the strip. Such fourth order polynomial roll gap profiles have improved strip quality yet still have not completely eliminated quarter buckle flatness defects particularly when the temperature of the rolls is high during high speed rolling and/or high reduction. In an multi-stand aluminum hot rolling mill, the strip typically enters the first mill stand at about 750° F. and exits the mill stand at about 650° F. The rolls are continually sprayed with a coolant such as a water and oil mixture. The centers of the rolls are typically about 215° F. and the edges of the roll are about 190° F. The temperature differences across the length of the roll (the temperature profile of the roll surface) causes varying expansion in the roll surface and hence, varying flatness in the strip. The temperature profile of the roll surface temperature changes over time as the mill stand heats up with use and eventually reaches a steady state condition.
Accordingly, a need remains for a system to compensate for the varying thermal expansion of the rolls in a strip mill stand to obtain a strip which is fiee fiom quarter buckle defects.
SUMMARY OF THE INVENTION
This need is met by the rolling mill stand of the present invention which includes a pair of rolls axially slidable relative to each other and configured to receive a moving strip of metal in a gap therebetween and defining a roll gap profile. Each roll has a ground roll profile wherein the diameter of each roll varies along the length of the roll according to the seventh order equation represented by EQ1
D(Z
R
)=C
0
+A Z
R
+B Z
R
2
+CZ
R
3
+D Z
R
4
+E Z
R
5
+F Z
R
6
+G Z
R
7
EQ1
wherein Z
R
is the normalized distance across the length of the face of the roll measured from the center of the roll. Preferably, the second order component of EQ1 is constant, most preferably, D is zero thereby eliminating the fourth order component from the roll shape. In the present invention, the roll gap profile formed by rolls ground to the specified shape can be adjusted to fully compensate for the effect of work roll thermal expansion and, thus, significantly reduce the formation of quarter buckles in the finished strip.
The rolling mill stand further includes a controlling system for adjusting the roll gap profile. The controlling system includes a thermal tracking system for determining the temperature profile of the rolls along the axial length of the roll and adjusting the roll gap profile based on the temperature profile. The rolls are cooled via a cooling spray system and are driven by a mill stand motor. The temperature profile is determined by modeling the temperature profile of the rolls based on the amount of coolant sprayed on the rolls and the amount of power delivered to the stand motor. The rolling mill stand further includes roll bending jacks and the controlling system further includes a mill set-up system for determining the bending and flattening of the work rolls and backup rolls caused by the force of the strip being reduced in the mill stand. The mill set-up system models the roll gap profile based on the roll temperature profile, deflection and flattening of the rolls and the desired flatness and profile of a strip exiting the rolling mill stand.
The present invention further includes a method of controlling flatness and profile of a strip rolled in a rolling mill stand having the steps of:
(a) providing a pair of side shiftable work rolls to form a gap therebetween, each roll having a ground roll profile wherein the diameter of each roll varies along the length of the rolls according to the seventh
Alcoa Inc.
Buckwalter Charles Q.
Levine Edward L.
Meder Julie W.
Tolan Ed
LandOfFree
Sixth order actuator and mill set-up system for rolling mill... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sixth order actuator and mill set-up system for rolling mill..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sixth order actuator and mill set-up system for rolling mill... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2599484